Authorities from the autonomous Kurdistan Regional Government (KRG) in northern Iraq have reportedly forced about 250 displaced Sunni Arab families to leave Kirkuk after Sunni sleeper cells were accused of helping Islamic State (ISIS/ISIL) jihadists carry out an attack in the Kurdish-controlled city.

Two days after the ISIS attack on the city of Kirkuk last Friday, the Kurds announced they would be expelling Sunni Arab families who had already been displaced by the war against ISIS in Iraq, reports Reuters.

“Just a few hours after the announcement we understand that around 250 civilian families felt they had no choice but to leave,” Lise Grande, the United Nations humanitarian coordinator for Iraq, told Reuters.

“The Sunni families, who had been sheltering in Kurdish-controlled Kirkuk province from the conflict with Islamic State, began moving out after authorities told them on Sunday to leave or face being forcibly expelled,” the news agency adds, citing humanitarian workers and residents.

ISIS is a Sunni group. Kurdistan authorities suspect ISIS terrorists who attacked Kirkuk last Friday were assisted by sleeper cells hiding among the displaced Arabs or even by Sunni residents in the city, the provincial capital of a province of the same name.

However, Grande said the UN had no evidence any of the families who were pushed out of the city had helped ISIS, adding that “the timing of the [Kurdish authorities] move suggested it was used as a pretext to force them out.”

“The United Nations is very concerned about any action that could be understood as collective punishment,” Grande told Reuters, noting that she was worried that the move could also set a precedent in a region suffering from ethnic and sectarian divisions.

Kirkuk is located about 100 miles from Sunni-majority Mosul, Iraq’s second-largest city and ISIS’s last major stronghold, located in the country’s Nineveh province.

Last week, U.S.-backed Iraqi government troops and their allies, which include KRG forces, Sunni tribesman, and Iran-backed Shiite militias, launched an offensive to retake Mosul from ISIS.

Reuters explains:

Kirkuk is the most disputed area of Iraq because of its complex population mix.

Kurds took full control of the province in 2014 after the Iraqi army retreated from an Islamic State takeover of much of the north of the country, and Arabs complain that Kurds have since flooded to Kirkuk to tilt the demographic balance in the event of a referendum on the status of the city.

At the same time, over 300,000 Sunni Arabs have sought refuge in Kurdish-ruled Kirkuk from the Islamic State jihadists.

“Sixty-three militants also died in the heavy fighting that lasted until Sunday, when authorities restored control,” notes Reuters, adding that “the jihadists carried out the operation to relieve pressure on Mosul.”

As the U.S.-backed Iraqi troops advance towards Mosul, the UN expects a mass exodus from the city over the next few days.

“We are very concerned because we estimate that there are more than a million civilians inside the city,” declared Grande. “And any time there is a major attack there could be a major outflow of people.”